The primary ingredient in a traditional shepherd's pie is ground lamb. This classic British dish typically consists of a savory filling made from lamb that's cooked with vegetables, such as peas and carrots, and seasoned with herbs. The meat is topped with a layer of creamy mashed potatoes, baked until golden brown. Shepherd's pie is often confused with cottage pie, which uses ground beef instead of lamb. The origins of shepherd's pie can be traced back to the early 19th century, and it remains a comforting and hearty meal enjoyed across many cultures today.